The aftermarket manifold will flow better than the factory manifold, generally. It's supposed to be a performance part.
If you go with a factory iron manifold, get the square one. The spread bore only works with a Motorcraft 4350 carb. You'll have many choices in carburetors with the square pattern.
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
ECO Green: '15 FCA Jeep Cherokee KL Trailhawk